The present invention relates to a process for isolating a polymer from a solution thereof, and more particularly to a process for isolating a polymer in the form of particle or powder by dispersing an organic solvent solution of a polymer in an aqueous solution of a water-soluble polymeric dispersant and distilling away the organic solvent.
Various processes for isolating or recovering a polymer from a solution thereof are known. For instance, for the isolation of aromatic polyester resins, there are proposed a process in which the resin is precipitated by adding a non-solvent such as methanol, ethanol or acetone to the solution, as disclosed in Japanese Examined Patent Publication (Tokkyo Kokoku) No. 5599/1962, No. 18399/1962, No. 1959/1964 and No. 14474/1967, a process in which an organic solvent solution of the resin is brought into contact with hot water or steam to distil away the solvent with steam, thus obtaining the resin in the form of a slurry in water, as disclosed in Japanese Examined Patent Publication No. 9445/1960 and No. 9446/1963, and a process in which an organic solvent is distilled away with heating under reduced pressure from the organic solvent solution of the resin, as disclosed in Japanese Examined Patent Publication No. 20746/1963. However, these processes have the disadvantages. The first process is uneconomical because of requiring a large amount of the non-solvent in general. The second stripping process is disadvantageous in that the bulk density of the isolated polymer is very small and, therefore, not only this results in poor economy in the subsequent washing and drying procedures, but also the pelletization of the resin is attended with difficulties. The last process by distillation is not practicable on an industrial scale, since the recovered resin becomes viscous gummy mass with increasing concentrations of the treated solution and it sticks to the wall of a vessel to result in lowering of the heat conductivity. In order to eliminate the disadvantages of these processes, it is also proposed to pulverize a gelled organic solvent solution of a polyester having a relatively high polymer concentration in Japanese Examined Patent Publication No. 41248/1980. This process is not always an industrially advantageous process, since special equipments such as a thin film evaporator and a kneader are necessary and a large power is required.
It is an object of the present invention to provide a process for isolating a polymer from an organic solvent solution thereof by a simple procedure.
A further object of the invention is to provide a process for separating a polymer from an organic solvent in a uniform particle or powder form having a high bulk density.
These and other objects of the present invention will become apparent from the description hereinafter.